Mercury pool electronic device



March 23, 1948. E. G. F. ARNOTT MERCURY POOL ELECTRONIC DEVICE Filed Oct. 26', 1946 Patented Mar. 23., 1948 MERCURY POOL ELECTRONIC DEVICE Edward G. F. Arnott, Upper Montclair, N; J., as-

signor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsyl- Vania Application October 26, 1946, Serial No. 705,896

7 Claims. 1

This invention relates to mercury pool electronic devices and more particularly to the dielectric ignitor therefor and method of manufacture of the same.

It has been recognized in the prior art that electrodes, generally referred to as ignitors, for initiating the arc in a mercury pool device, the most common form of which is known as an ignitron, can be made by coating a metal rod with a layer of glass and locating said rod so that at least a part thereof is immersed in the mercury pool. Ignitrons made in this way have relatively short life due to eventual puncture of the glass coating resulting from erosion of the surface of the glass next the mercury. In many cases this erosion occurs all around the ignitor at the meniscus of the mercury, before finally puncturing. The voltage and energy required to fire such an ignitor depend on the thickness of the coating and also on the capacity of the ignitor to the mercury at the immersed part of the ignitor.

In its broad concept, the present invention has for an object the provision of an ignitor overcoming the noted deficiencies of prior art ignitors.

More specifically, an object of the invention is to provide an ignitor minimizing erosion in operation and promoting long life of the device in general.

Another object of the invention is to provide an ignitor requiring a minimum of applied energy for operation thereof.

Other objects of the invention will appear to those skilled in the art to which it appertains both by direct recitation thereof and by implication from the context as the description proceeds.

Referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout the'several views;

Figures 1 and 2 are vertical sectional views of two embodiments of the present invention as incorporated in an electronic device of the mercury pool type; and

Figure 3 illustrates by curves the relation of voltage and time of application of this voltage for both embodiments of Figs. 1 and 2 for purpose of comparison.

In both Figure 1 and Figure 2, a closed envelope IE! is provided which preferably comprises a basal cup-like portion I l, a head portion l 2 thereabove, both preferablyof glass, and an intervening neck or metallic cylinder l3" sealed at its end peripheral margins to the basal and head portions respectively. Said head portion I2 is preferably reentrant, as at I4, at its upper part so as to provide a downwardly directed margin within the outer wall of the head, and from this reentrant portion I4 depends a cup-shaped anode [5. The said' downwardly directed margin of the reentrant part of the head is sealed to the upper edge margin of the cup peripherally thereof. For convenience of manufacture, said basal and head portions and anode are all geometrically bodies of revolution and situated on a common axis. The bottom wall iii of the cup is accordingly in a plane perpendicular to the axis, and as in use the device is positioned axially vertical, said bottom wall of the cup is normally horizontal. As shown, the plane of the bottom wall of the cup is approximately at the level of the plane of the upper peripheral edge of the neck or metallic cylinder is. Furthermore, the spacing of the cylindrical side wall of said cup is preferably proportioned to situate said wall reasonably near the outer wall of the head'portion for discouraging discharge in the annular space I 1 around the cup and thereby constitute the under surface of the'bottom wall of the cup'the effective anode portion of said cup.

A pool is of mercury or equivalent material is located within the envelope, and as shownsaid pool fills the basal portion H and extendsabove the same to a level well above the bottom edge of the neck or metallic cylinder l3, preferably substantially to a level half way up the said metallic cylinder. Said pool constitutes the oathode for the device and has electrical connection to the exterior as by means of arod or terminal l9 therein coaxial to the said basal portion and appropriately projecting downwardly through and sealed to the basal portion. The upper end of said rod or terminal l9, while located in said pool, is well below the upper surface of the pool so that discharge will occur from the pool surface only. It may now be observed that a relatively short spacing is obtained between the oathode surface at the top. of the pool and the anode surface at the bottom of the anode cup andthat said surfaces are substantially in planes parallel to each other and provide a discharge region therebetween; this structure being particularly desirable for high voltage high frequency operation for which the device is intended.

The ignitor for instigating discharge comprises said metallic cylinder or neck l3. Since said cylinderembraces diametrically a larger part of the discharge region than that occupied by the anode, and is on a common axis with the anode, it does not interfere with the close spacing of the anode and cathode and yet has a desirable proximity the envelope. In Fig. 2, said dielectric coating 20' covers the entire inner surface of the metal cylinder between the top and bottom sealed margins. acteristics as will appear hereinafter. In either construction, a large surface area for the ignitor and a high capacity are obtained.

While any suitable dielectric such as glass and metal may be used for the several parts of the device, it is of course very desirable to employ materials which have substantially the same coefficients of expansion so as to assure permanent seals between the glass and metal and to avoid cracking of the glass. Acceptable glass and metal for the purpose are described in U. S. Patent No. 2,062.335 of December 1, 1936. Metal made in accordance with this patent is available on the market under the trade name of Kovar. The boro-silicate glass used with that specific metal is likewise available in two grades known in the tradeas Corning 704 glass and Corning 705.2 glass.

According to the specific embodiment of the present invention, the ignitor of Fig. 1 is made of the nickel-cobalt-manganese-iron alloy as described in said patent. Preferably before assembly of the ignitor cylinder with the basal and/or head portions of the device, said cylinder is inside coated part way of its length with, for instance, Corning 705.2 glass, leaving an uncoated band 2! next the other end of the cylinder. The coating is very thin, being only a small thickness compared to the thickness of the glass used in making the container wall and may be specifled as of the order of 0.1-0.5 mm. thickness. This thin coating may be applied by spraying the glass on the Kovar cylinder, and heating it, thus giving a uniform coating of the desired thickness. r

In like manner, the specific embodiment of the invention illustrated in Fig. 2 comprises a cylinder of the nickel-cobalt-manganese-iron alloy previously identified herein. Likewise preferably before assembly of the ignitor cylinder with the basal and/or head portions of the device, said cylinder is inside coated, but in this showing, for its entire length with for instance Corning 705.2 glass. Thickness and mode of application of this coating is the same as above described with respect to Fig. 1. In both showings, the sealing of the basal glass portion is made at the rim of the coated ignitor cylinder and in part upon that coating. Similarly in Fig. 2, the head'portion of glass is sealed at its edge to the coated margin of the ignitor cylinder. An especially tenacious bond is obtained by sealing to the Kovar over the coating of glass thereon. In both forms shown of the invention, the metallic cylinder [3 is self-sustaining to withstand pressures resulting from evacuation of the envelope, and likewise sustains the coating 20 thereon which could not, of itself, withstand such pressure.

Ignitors as described above utilizing glass for the dielectric inside coating of Kovar cylinders, have been made and operated at 3 kv. 115- This difference affects the operating charing a 10 to 1 step up transformer. A condenser of .005 microfarad charged to 300-500 volts was discharged through the primary of the transformer. The prior art ignitor referred to at the beginning of this specification comprising a dielectric coated rod requires a condenser of 16-30 microfarads for similar charge. Thus the energy required by the ignitor of the presentinvention is less than t of that required by the mentioned prior art ignitor.

, f Comparative operation of the ignitors shown in Figures 1 and 2 is illustrated by the curves of Figure'3; These curves show the applied voltage and time duration thereof on the ignitor, the solid line curve applying to the construction of Fig. 1, and the broken-line curve applying to the construction of Fig. 2. By virtue of the exposure of the band of the ignitor metallic cylinder above the coated portion of said cylinder the initial igniting arc instigated across the dielectric of the ignitor quickly passes or spreads to the exposed metal of the ignitor which acts momentarily as an anode in transition of the arc to the main anode. The vertical part Of curve A' shows this prompt and complete transfer of the arc and resultant ignitor-voltage cut-off. In the construction of Fig. 2, since no discharge occurs until the arc to the main anode starts, the ignitor voltage is not dissipated by a preliminary are as in the construction of Fig. 1, but remains on the ignitor until the constants of the ignitor firing circuit allow it to return to zero which is indicated by the sweeping downward right-hand portion of curve B. r

The ignitor of Figure 1 has the advantage of being subjected-to voltage stress for only a'very short time, which decreases likelihood of failure. Figure 2 structure has the advantage of complete internal coverage of the metal portion of the ignitor cylinder, which, being an alloy presents the possibility in Fig. 1, where internally exposed, of releasing oxygen or other gases during and to the detriment of operation of the device. V v r I claim: e

1. In a discharge device having an envelope, a pool cathode and an anode spaced therefrom and with a discharge region between the cathode and anode, an annular ignitor constituting a sustaining part of said envelope and coaxial with the cathode and anode, said ignitorihaving a conductive portion and an internal dielectric coating thereon and sustained thereby and in part engaged by said pool cathode and in part exposed to said discharge region and said pool cathode being maintained out of contact with said conductive portion of the ignitor by said dielectric coating. 7

2. An electronic discharge device comprising an envelope, a pool cathode, an anode spaced from said cathode, said device providing a discharge region between the cathode and anode, an annular ignitor constituting a sustaining part of said envelope and coaxial with the cathode and anode, said ignitor having a conductive portion and an internal dielectric coating thereon and sustained thereby and in part engaged by said pool cathode and in part exposed to said discharge region, said conductive portion also being in part exposed to said discharge region.

3. An electronic discharge device comprising an envelope, a pool cathode, an anode spaced from said cathode, said device providing a discharge region between the cathode and anode,

an annular ignitor constituting a sustaining part of said envelope and coaxial with the cathode and anode, said ignitor having a conductive portion and an internal dielectric coating sustained thereby and covering the entire inner surface of said conductive portion in part above and in part below the surface of said pool cathode, said pool cathode being maintained out of contact with said conductive portion of the ignitor by said dielectric coating.

4. An electronic discharge device comprising an envelope having a cupped basal portion and a head portion with a reentrant portion thereby providing outer and inner walls, an anode sealed to the inner wall, a cylindrical ignitor constituting a sustaining part of said envelope and interposed between and sealed to the outer wall and to said cupped basal portion, and a pool cathode in said basal portion.

5. An electronic discharge device comprising an envelope having a cupped basal portion and a head portion, both said basal portion and head portion being of non-conductive material, said envelope having a conductive portion between and sealed to both said basal portion and head portion and constituting a sustaining part of said envelope, an anode sealed to said head portion, and a pool cathode in said envelope and in part in said conductive portion, said conductive portion having a dielectric material thereon and sustained thereby and located between the conductive portion and the pool cathode.

6. An electronic discharge device comprising an envelope having a cupped basal portion and a head portion, both said basal portion and head portion being of non-conductive material, said envelope having a conductive portion interposed between and sealed to both said basal portion and head portion and constituting a sustaining part of said envelope, an anode sealed to said head portion, said conductive portion having a dielectric coating on the entire surface thereof within the envelope from the basal portion to the head portion and sustained by said conductive portion, and a pool cathode within said basal portion and in part within said conductive portion and maintained out of contact from said conductive portion by the said dielectric coating.

7. The herein described method of manufacture of an electronic device comprising coating a conductive cylinder on the inner face thereof with a dielectric material, sealing a basal cup to said cylinder and overlapping said coating of dielectric material at an end margin of said cylinder, and sealing a head portion to the other end margin of said cylinder.

EDWARD G. F. ARNOTI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,163,706 Thomas Dec. 14, 1915 2,205,225 Slepian June 18, 1940 2,299,094 Klemperer Oct. 20, 1942 

